Check for a GET variable in URL

so I'm making a simple log in form in my site using Jade and ExpressJS. It's all working, the only problem I'm having is when the user enters incorrect log in details. When they enter wrong details I redirect them to the log in page with a parameter in the URL (

/admin?falseLogIn

). My question is: how can I check if this GET variable exists in my jade view?

Reasoning. I don't think it's good practice to parse your url query directly in your view. While that is fine for raw php like your example using $_GET, if you use a MVC framework, like Laravel for example, you quickly move away from that. Let the controller do its job of handling logic based on queries and handing off the relevant information to views. Then in your view, its should be simple presentation logic.